Amplifier apparatus for high energy particle accelerators



June 30, 1964 R. H. RHEAUME ETAL 3,139,591

AMPLIFIER APPARATUS FOR HIGH ENERGY PARTICLE ACCELERATORS Filed Jan. 16, 1961 5 Sheets-Sheet l OUTDOOR EXPERIMENTAL AREA G 9 WL y 2 mm mw L Dn E NIIYY EN IA U AT o G m m D a N A S nlu E NFB EOM DI T D MKV D NE P nlv OC R TR @E L P AU7 OR WW2 3E P //w w OII m 2 H// 2 \l U C 3@ /I 6 3 w LINEAR ACCELERATOR c. OT RE mw. :mn GR u o UP,A BWM.. EIS mmm V RTW ESA Mum ML C FS 8 G Om 2 UN mm /Q Gl T Mw m8 W IN .B mm M sw WH BL OC WHL NC N R EA U D. 6 T 5 XF. 2 T m. R E w. w 7 2 umM S W T U @wm m I\H\\ HUG Wo f BOA 2 RRM M O HO N T 4 U 2 FEET BOO IOOO GOO IOO

June 30, 1964 R. H. RHEAUME ETAL. 3,139,591

AMPLIFIER APPARATUS FOR HIGH ENERGY PARTICLE ACCELERATORS 3 Sheets-Sheet 2 INVENTORS RAYMOND H. RHEAUME ROBERT E. ZIDER FRANK A. JANIK BY AMPLIFIER APPARATUS POR HIGH ENERGY PARTICLE ACCELERATORS Filed Jan. 16, 1961 R. H. RHEAUME ETAL June 30, 1964 3 Sheets-Sheet 3 n l alii @S @zw I E m05 mE/m6 a4 mgm ad 02m INVENTORS FRANK A JAN|K RAYMON H. RHEAUME ROBERTE ZIDER United States Patent Office Patented June 30, 1964 3,139,591 AMPLIFIER APPARATUS FOR HIGH ENERGY PARTICLE ACCELERATRS Raymond H. Rhaume, Centereach, Robert E. Zider, Baldwin, and Frank A. Janik, Medford, N.Y., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Jan. 16, 1961, Ser. No. 83,125 Claims. (Cl. S30-119) This inventiotn relates to amplifiers and more particularly to the amplification of power in accelerators capable of accelerating atomic particles to high energy levels.

lt has been discovered that atomic particles can be accelerated to high energy levels and directed at target atoms to produce momentarily kmany new particles such as mesons which are of intermediate masses between the electron and proton. Also, anti-matter or antiparticles have been produced in such a way and it has been believed that the production of such particles and materials may hold the key to the basic structure of the nucleons which make up an atomic nuclei.

It has been found that cosmic radiation has produced such particles as mesons but the mesons that have been studied from this source have been in existence for brief periods of time measured in millionths of a second or less. Moreover, the source of primary cosmic rays in space has made it diflicult to study the mesons produced thereby. It has thus been universally recognized that high energy accelerators have been necessary to produce the mentioned particles and materials under controlled conditions.

An early high energy particle accelerator produced particles having up to about 80,000 electron volts energy. Later similar devices grew successively larger until multimillion electron volt particle energies were achieved. Still later devices, such as the Brookhaven Cosmotron and the CERN Synchrotron, have achieved multi-billion electron volt particle energies.

Conveniently, the high energy accelerators known heretofore have employed an evacuated hollow substantially torus shaped endless tube and particles have been accelerated therein by at least one radio-frequency accelerating means placed around the tube at an accelerating gap in a confining magnet. The magnet substantially encircled the tube along most of the length of the tube and has been adapted to guide the particles around the tube as the particles have been accelerated. Advantageously, the particles have been injected into the tube at relatively low energy levels and a radio-frequency low power command signal has been amplified and applied to the accelerating means to produce a travelling wave of radiofrequency electrical ield that travelled with the speed of the injected particles as the particles orbited past the accelerating means. Thereupon the frequency of the command signal and signal amplified therefrom have been increased over a broad band of video-frequencies to increase the speed of the wave and the speed of the particles as they orbited past the accelerating means. For.

amplifying the command signal a radio-frequency amplier has been required, that has been capable of good transient response and the production of broad band, high power, video frequency signals of pure wave form.

Conventional audio-frequency amplifiers known heretobroad band of video-frequency signals (le. frequency v from 1 megacycle per second to 5 megacycles per second) at such a high power level. This has been true particularly with amplifiers having air-core solenoid interstage coupling networks.A Also conventional amplifiers have been complicated and expensive. As an illustration, grounded cathode amplifiers have had a large number of expensive and large vacuum tubes, have required high direct current plate power input and have been subject to parasitic oscillations and undesirable instabilities such that complicated and expensive neutralization and series and shunt peaking have been required.

This invention contemplates the combination, in a high energy particle accelerator, comprising a multi-stage arn- .plilier having low power push-pull grounded cathode operated tetrodes, high power push-pull, grounded-grid operated triodes, and interstage autotransformers for coupling the stages of said amplifier, comprising split ringshaped ferrite cores formed with gaps that bisect said cores normal to the plane of said cores, said ferrite having a high permeability, a low power loss factor, and centertapped voltage-step-down windings tightly encircling said cores and extending equal distances from a point on each of said cores equal distances from said gaps with small spacing between said windings.

The above and further novel features of this invention will appear more fully from the following detailed description when kthe same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

FIG. 1 is a partial top view of the high energy accelerator of this invention.

FIG. 2 is a partial schematic viewy of the energizing and control means for the apparatus of FIG. 1.

FIG. 3 is a detailed schematic of the amplifying means of FIG. 2.

' FIG. 4 is a partial isometric View of the interstage autotransformer of FIG. 3. y

FIG. 5 is a partial isometric view of the tuning means for the autotransformer of FIG. 4.

Referring to FIG. 1, accelerator 11 comprises generally non-magnetic endless tube 13, means 19 for evacuating tube 13, a particle source 21, means 22 for accelerating and injecting energetic nuclear particles, advantageously protons, into tube 13, magnetic means 26 partially shown schematically for ease of explanation for guiding the parhigh energies to produce reactant particles such as mesons,

hyperons, neutrons, protons, anti-nucleons, and other products such as those mentioned above. Auxiliary hitting the walls of tube equipment for analyzing the reactants includes means 31 in the target building 29 such as bubble chambers photographic emulsions, and counters such as scintillation counters.

Advantageously, the particle source 21 has a small chamber lilled with hydrogen gas and an electrical arc. The arc discharge ionizes the hydrogen by tearing electrons oft the hydrogen atoms and produces hydrogen nuclei or protons with positive charges. The protons pass through a small aperture in the mentioned chamber and into means 22 for accelerating the protons.

Accelerating means 22 advantageously includes a preinjector 32 comprising a conventional Cockcroft-Walton type generator in which a live stage voltage multiplier operating from a direct current transformer, builds up large potential differences and applies them across an evacuated accelerating tube so that protons travelling down the tube receive an amount of energy equivalent to the potential difference across the tube. The protons receive an energy of about 75 thousand electron volts and pass into a buncher cavity 35.

The buncher cavity 35 receives the accelerated protons from the pre-injector 32 and pre-bunches the protons received thereby to match the entrance requirements of the injector-accelerator 36. The accelerator 36 is conventional and advantageously is like the one described in United States Patent 2,874,326, comprising a radio-frequency structure approximately ninety centimeters in diameter, and thirty-three meters long, and twenty-four drift tubes through which the proton beam from the preinjector 32 passes. Pulsed quadrupole magnets (not shown) located inside the drift tubes focus the proton beam and a 200 megacycle pulsed radio frequency source having a peak power of about tive megawatts, a width of about 200 microseconds and a repetition rate of five peaks per second excites the accelerator 36 to increase the proton beam therein to about fifty million electron volts.

Thereupon a conventional debuncher 37, following the accelerator 36, reduces the energy spread of the proton beam and an injection system having a deflector, focuser and monitor inject the beam into tube 13 at closely controlled conditions, for example, at an energy of fifty million electron volts i--2 percent at a speed of about onethird the velocity of light, at a pulse width of seven microseconds, at an angular spread less than itwo milli radians and at a proton content of about 1010.

Magnetic means 26 bend the particles 23 into circular paths around tube 13 and prevents the particles from 13. Advantageously, magnetic means 26 strongly focuses the beam of particles 25 in one plane and simultaneously defocuses in the other plane. This system, known as the alternating gradient synchrotron system, has been shown to yield a net strong focusing force and has required only about 4,000 tons of steel for the magnets. When the particles are injected into tube 13 the magnetic lield produced by magnetic means 26 is about 120 gauss. The magnets thereof provide a ield of uniform azimuth around tube 13, having a gradient of about per inch, and maintain their field patterns from 120 gauss to about 13,000 gauss. Since the latter requirement cannot be met sumciently well without correction auxiliary correcting magnets are included at sixty points around tube 13. Apparatus like magnetic means 26 and its auxiliaries is described in The Brookhaven Alternating Gradient Synchrotron by R. A. Beth and C. Lasky,

The particles injected into tube 13 and guided by magnetic means 26, are accelerated to energies as high as over thirty billion electron volts and to speeds of up to a few tenths of a percent less than the speed of light. To this end, there are advantageously twelve radio-frequency accelerating stations or means 27 at spacedV intervals around tube 13. Each accelerating station 27 has a double tunable radio-frequency cavity that imposes acin thegDecember 5, 1958 issue of Science'.

said core equal distances from said celerating electric forces on proton bunches at each passage of a station by means of a pair of accelerating gaps about four feet apart in the wall of tube 13. At each passage, each station advantageously accelerates the protons 8,000 volts and for this purpose high total peak radio-frequency amperes are required by accelerating means 27. As the energy of the particles increases the velocity of the particles increases rapidly at rst and then more slowly as the protons approach the velocity of light. Due to the velocity increase, the transit time of each particle around tube 13 will decrease. Thus the frequency Isupplied to the accelerating stations 27 must be increased so that the protons will arrive at the gaps in the right phase to experience a forward accelerating impulse. Because the accelerating means 27 accelerate the particles from less than one-third of the velocity of light to within a fraction of a tenth of one percent of light velocity the frequency of the accelerating must increase over a broad range of frequencies, eg., from 1.4 to 4.46 megacycles per second.

Referring to FIG. 2, the high power, broad band of video-frequencies required by accelerating means 27 must be regulated in phase and amplitude in order that the energization of the accelerating means 27 is synchronized with the movement of the particles in tube 13. To this end, a suitable low power, broad-band, video-frequency command signal source connected to an induction pickup d2 around tube 13 supplies incable 43 a command signal of the proper phase and amplitude that must be boosted in power level and supplied to accelerating means 2'7 While maintaining a substantially linear (coaxial-cablelike) amplitude and phase response to the input cornmand signal in cable 43. For example, a charge is induced in pick-up 42 every time a bunch of protons passes the pick-up and this charge is supplied as a 1 watt, 2 volt, 1.4 to 4.46 megacycles per second command input in cable 43 properly synchronized in phase and amplitude eg. by suitable lead length compensating means 40 when several leads are employed. The command signal must be amplified to about eighty peak kilowatts, 120 peak arnperes and 1400 volts while maintaining a wave form that corresponds in phase and amplitude substantially perfectly with the input command signal. Then when the amplified signal is supplied to accelerating means 27 and the particles in tube 13 pass thereby, the accelerating means 27 bunch the particles in tube 13 and impart progressively greater and greater energies to the particles each time they pass an accelerating station 27.

Conventional ampliers known heretofore have not been capable of supplying high enough power levels, have not been capable of supplying a broad-range of videofrequency signals, have been unduly inefficient, expensive, or complicated, have required a large number of expensive and large vacuum tubes, high direct plate power input and have been subject to parasitic oscillations and undesirable instabilities such that complicated and expensive neutralization and series and shunt peaking have been required.

Referring now to FIG. 3, this invention provides in high energy particle accelerator 11 the combination comprismg a high power output amplifier 44 having pushpull grounded cathode connected tetrodes in a first section 46, push-pull connected triodes having groundedgrids in a second section 54, and interstage autotransformers A for coupling the stages of said amplifier 44, comprising a split-ring-shaped ferrite core forming gaps 1n a plane that bisects said core normal to said core and having a high permeability, a high quality factor and tightly wound, closely-spaced, center-tapped voltage-stepdOWfl windings CXeHdIlg equal distances from a point on gaps.

44 takes a low power, single ended command in- The first section 46 of amplifier broad-band, video-frequency,

` put such as described above, in coaxial cable 43 and converts the single ended input into a double-ended push- V44 and ferrite-cored autotransformer fabricate is a rectangular cross-section,

,with end tap 75 and plate 77 connects with opposite end tap 79 of autotransforrner 81.

In order to preserve the waveform of the command signal in this amplifier 44, not only must the relative amplitude of the various frequency components be controlled, but the relative phase deviations of the various frequency components must be minimized and held essentially linear with frequency throughout the frequency band of interest. If there is substantial departure from linearity in phase vs. frequency response, the time of propagation of all frequency components through an amplifier will differ appreciably and synchrotron phase control difficulties will ensue. lt is significant that for the range of frequencies which encompass a phase deviation from about degrecs leading to degrees lagging, where the amplifier 81 of this invention are employed, even at high power tion is essentially linear with frequency. In contrast, the extent of the range of phase deviation is a full 75 degrees leading to a full75 degrees lagging when conventional air core autotransformers are used for the range of frequencies contemplated by this invention and the phase deviation is not linear with frequency. Thus, when waveshape fidelity, as determined by freedom from distortion, is required over a broad-band of frequencies, the air core yautotransformer is not satisfactory.

The mentioned autotransformer 81 has high ycoupling coefficients. For example, the side-to-side coupling coefcient is 0.94 andthe primary to secondary coupling coefficient is 0.98. Such high coupling coefficients have not been kpossible in autotransformers known heretofore, and are provided in accordance with the novel design and configuration of the autotransformer of this invention. To this end, autotransformer 81 is a center-tapped voltage step down transformer having primary windings 83 and 8S with a common center tap S7 and secondary windings 89 and 91 with respective side taps 93 and 95. The Windings have a suitable insulation such as a polyurethane insulation, minimum spacing between their coils, and low series leakage inductance, i.e., minimum voltage drop, without insulation break down at high frequencies or shunting at low frequencies. The windings are tightly wound on a first semi-circular section 101 (FIG. 4) of ferrite core 57 having a second semi-circular section 102 spaced from the first section 101 so as to form opposite gaps 103 and 104 equally spaced from the mentioned windings. Advantageously the gaps 103 and 104 are disposed l80 apart and normal to the plane of the vertical axis of core 57 so as to bisect the core and an adjustment means 105 equally adjusts the spacing therein. The gaps are not for impedance stability but are for tuning and to this end the windings have sufficient impedance so that varying the spacing of the gaps changes the autotransformer inductance. The inductance is changed in this manner without essentially changing the side-to-side and primary-to-secondary coupling coefficients. The cross section of core 57 has a short vertical axis and a long horizontal axis normal to the center of the vertical axis to provide maximum ferrite essentially at a constant radius. A suitable cross-section that is easy to but an elliptical cross section is also acceptable.

Conventional magnetic core tivity, such as iron, steel, Alnico, permalloy, permivar, or iron powder materials with low resismolybdenum permalloy,

imbedded in an inlevels, the phase deviameasured as sulating matrix are not suitable for core 57. Likewise, non-magnetic materials, such as non-magnetic metal, plastic, ceramic, glass, and air or a combination thereof are not suitable core materials. Advantageously, the ferrite core 57 of this invention has a high radio-frequency permeability. For example, the permeability must be over 300 which permeability is in a range that is commercially available. When the radio-frequency permeability is a constant times the ratio of the flux density to the magnetizing force and expressed as a value compared with the permeability of air, `the permeability of the ferrite material suitable for the cores of this invention should be greater than 300. Although higher permeability is available, physical limitations for adjustment of gaps 103 and 104 make it undesirable to have permeabilities that are too high. Also, higher permeabilities in the range of 3000 to 4000 would offer slight incremental advantage over currently available ferrite having permeabilities of 300 to 400. n

An additional requisite for 4the ferrite is a high quality factor or Q value of 20 or over, i.e., low radio-frequency `rite can be cooled easily,

ycombination with a multi-stage, l t quency amplifier, as will be understood 1n more detail v connect respectively with control grids of tubes losses and a low powerloss factor. A Q value of 2 or lower creates severe heat losses in the ferrite and is inop-z erable in accordance with this invention. A ferrite having a Q value of l0 is still undesirable from this standpoint. However, with a ferrite having a Q of 20 or over, the fere.g., with a 100 c.f.m. air blower even when the autotransformer is passing kilowatts of video-frequency power. An advantageous ferrite for core 57 is the Ferroxcube IV H brand of ferrite made by Philips, Eindhoven.

The described variable-gap ferrite core autotransformer 81 has the advantage of a higher current gain and impedance match, for example between a high impedance `moteness of the windings from gaps insures that the electromagnetic field is essentially enclosed within the ferrite core of the autotransformer of this invention. Consequently, the autotransformer of this invention makes possible a simple, inexpensive, and effective apparatus in broad band, video-frefrom the following.

. As shown in FIG. 3 the output side of taps 93 and 95 of autotransformer 81 energize push-pull, multi-grid tubes 106 and 107 balanced to ground. Side taps 93 and 95 106 and 107 having suppressor grids that are grounded. The cathodes of the tubes are connected with an input signal through a line 10S having a suitable direct current source shown in part. The output of tubes 106 and 107 increases or decreases in power in a manner corresponding to the command of the input signal therefor from autotransformer 81 which in turn corresponds with the `output from tube 63 and the input to tube 63 from line 43. Thereupon the output of tubes 106 and 107 energizes push-pull, multigrid tubes 109 and 111 balanced to ground through their screen grids and having low impedance inputs. Tubes 109 and 111 are advantageously class A1 operated 6CL6 pentodes having a high impedance output, with substantially linear amplitude and phase response to the input to tubes 109 and 111.

81 with low impedance control grids of two push-pull, multi-grid power amplifying tubes 117 and 119 balanced to ground rough their screen grids. Tubes 117 and 119 are advantageously class Al operated type 4X250 B tetrodes having indirectly heated cathodes and suitable B-iand B- energy sources (notshown). Advantageously, tubes 117 and V1199 have a suitable cathode follower screen grid potential feed such as provided by an 807 pentode 121. Tubes 117 and 119 produce a high impedance output having substantially linear amplitude and phase response with the input to tubes 117 and 119.

The outputs from tubes 117 and 119 connect through an interstage autotransformer 123, like the autotransformers described above, with low impedance control grids of two push-pull, multi-grid, power amplifying tubes 125 and 127. Tubes 125' and 127 are class A1 operated, 4-1000 A tetrodes having their cathodes directly heated by suitable high leakage inductance filament transformers. The filament transformers protect the free hung filaments of the tubes from collapse due to cold current inrush and have suitable power sources (not shown). Tubes 125 and 127 also have a suitable cathode follower screen grid potential feed provided by a 4-1000 A tetrode 128. Also, a ferrite cored center-tapped choke 129 advantageously cross-couples the inputs to the control grids of tubes 125 and 127 to clean up the wave form of the inputs by minimizing even-order harmonics, while simultaneously introducing D C. grid bias potential. To this end, the windings of the choke 129 have closely spaced tightly wound turns on an annular ferrite core having a vhigh permeability and a low power loss factor like the cores of the autotransformers described above. Thus the ferrite core of choke 129 is the same as the ferrite of the autotransformers described above and has a permeability of over 30() and a high Q of over 20.

The plates of tubes 125 and 127 have a high impedance and their output corresponds linearly with the input to their grids. The plates of tubes 125 and 127 connect through an interstage autotransformer 131, like the ones described above, with low impedance control grids of `two push-pull, multi-grid, power-amplifying tubes 133 and 135. The tubes 133 and 135 are class ABZ operated standard commercial 4CW 10,000 A tetrodes having a suitable B-lpower source (not shown) for their screen grids, and their cathodes are directly heated by filament transformers like those described above. A ferrite cored centertapped choke 137 like choke 129 connects the control grids ofthe tubes 133 and 135 and plates of the tubes 135 and 133 provide a high impedance output having an amplitude and phase corresponding linearly, with the input to tubes 133 and 135.

`The described multi-grid amplifying tubes of the first amplifying section 46 of amplifier 44 have the advantage that they are readily available, relatively inexpensive, durable and reliable at low power levels compared with t the present low power triodes. Also the described multigrid tubes act as a phase buffer to keep output cable termination phase perturbations from failing back fromr the grounded grid tubes in the second section of amplifier dddescribed in more detail hereinafter. The described autotransformers have the advantage that the tubes connected therewith have enhanced gain-band width capabilities at video frequencies, smaller and fewer tubes can be used therewith than in conventional amplifiers, and the interstage circuitry thereof provides substantially linear phase change with frequency with simpler interstage circuitry than in the amplifiers known heretofore. The autotransformer of this invention also provides means for making rapid and effective changes in inductance tuning in the autotransformers of this invention and their associated circuits without appreciably affecting the` coupling coefi'icients of the autotransformers. Also high coupling coefficients can be obtained without disproportionately increasing the distributed capacitance.

,cooling means such as are '75l The high impedance outputs from the plates of tetrodes 133 and 135 energize low impedance cathodes of two push-pull class B2 operated grounded-grid standard commercial power triodes 139 and 141 forming the beginning of the amplifying section Se. In this stage the high cross coupling coeflicient provided by the ferrite autotransformer of this invention affords economy of high voltage plate DC. input current and minimum anode dissipation without appreciably deteriorating the radiofrequency wave form from that of class A operation. To this end, a ferrite cored autotransformer 143, like the autotransforniers described above, is interposed between the output plates of tetrodes 133 and 135 and the input cathlodes of triodes 139 and 141. Also, two filament transformers like those described above, having a suitable power source (not shown) are interposed between the output side taps of the autotransformer 143 and the input cathodes of triodes 139 and 141. Additionally, a split ferrite cored cathode choke 14S, like the chokes described above, in other respects, connects the push-pull outputs of the autotransformer 143 to maintain a clean wave form input to the mentioned filament transformers connected to the cathodes of triodes 139 and 141. Thus, it is understood that the input to the cathodes of triodes 139 and 141, and amplifying section 54 is a double-ended, push-pull, broad-band, video-frequency, relatively low impedance, balanced-to-ground, input signal of intermediate power level. lt is also understood that this input signal to triodes 139 and 1111 corresponds substantially linearly inamplitude and phase to the relatively low power input command signal in coaxial cable 43, the input command source for the first section i6 of amplier 44 and thus the input to tricdes 139 and 141 is also an input comrvmand signal.

.with this'invention with no grid bias source required because of the combination with the described ferrite autotransformer of this invention. The triodes 139 and 1d-1 are advantageously of the ML-6424 type. The triodes 131 and `141 have high impedance output plates 151 and 153 connected through end taps of a center-tapped ferrite cored interstage autotransformer 155, like the ones rdescribed, above, with subsequent low impedances provided by cathodes of stable ground-grid, push-pull connected, class-.B2 operated triodes 157 and 151i. The center tap of the autotransformer is radio frequency lgrounded thru a suitable capacitor and has a suitable B-lsource (not shown). This system in combination with the multi-grid tubes of section 16 described above, which act as buffers to keep output cable termination vphase perturbations from tailing back from the triodes has thetadvantage of great stability and simple, low cost, reliable circuitry with readily available standard components for high power output, broad-band, video-frequency appiications where good transient response is essential, such as in high energy accelerator 11.

in the present, as well as the succeeding amplification stages, amplification takes place in interstage, ferritecored voltage step-down,autotransformers which are like those described above. The autotransformers of the presentand succeeding stages have typically a 3:1 voltage step-down ratio in the saine configuration as the above-described autotransformer windings. It is understood that succeeding autotransformers increase progressively in size and have larger tuning means. Additionally, the coils of 'at least the last autotransformer have provided by hollow windings having means (not shown) for circulating a cooling fluid 9 therethrough.l This is to offset skin 'effect heating in the copper coils rather than for cooling the ferrite.

The core of autotransformer 155 is like the autotransformer cores described above and in this regard is made of a ferrite that must possess high radio-frequency permeability and low radio-frequency losses, i.e., a high Q or quality factor. The form of the cores in the present and upper amplification stages is the same as the previously described autotransformers. Thus the autotransformers herein have split-ring, shaped cores forming gaps which bisect the core in a plane normal to the vertical axis of the core. The cores herein, additionally advantageously comprise a plurality of closely stacked coaxially adjacent semi-circular segments separated by 0.15 polytetrafiuoroethylene wafers that protect the segments from. the high turn-to-turn voltage and high transient voltage in the autotransformers. Advantageously, an insulating tape, such as polyester tape, having high mechanical and electrical insulating proper-ties, ties six or more of the segments together, to form U-shaped semi-circular sec- .tions 101 and 102. j The segments of this and later stages are large and the tuning means 105 therefor is substantially the same as the tuning means for the previously described autotransformers, and opens and closes the autotransformer gaps equally. Particularly, the tuning means 105 for the autotransformers of this and the next stages comprise a rectangular box shaped linen base phenolic housing 171 held together by nylon screws at its sides. A rectangular phenolic block 173 fastened inside of the housing near its top supports one of the semi-circular sections. The other section rests adjacent to the bottom inside of the housing. Phenolic vice jaws 175 and 177 on the bottom inside of housing 171 support the second section 102 and holds the open ends thereof facing upwardly adjacent the downwardly facing open ends of section 101 to form gaps 103 and 104. Brass left and right threaded screw 183 rotates in a housing 171 and threads in opposite directions into vice jaw 175 and 177 so that rotation of the screw 183 in one direction, closes the jaws to raise second section 102 and reduce the distance across gaps 103 and 104 be- `tween sections 101 and 102. Rotation of screw 183 in the opposite direction opens jaws 175 and 177 so that section 102 falls to increase the opening of the gaps. A pheolic key 178 secured to the inside curved portion of the second section and fitted into slots 184 on opposite sides of housing 171 guides the up and down movement `of section 102 so as to maintain'a spacing in gap 103 that always equals the spacing in gap 104. The purpose of the prescribed adjustment means is to adjust the total inductance without essentially degrading the high coupling coefficients, and to tune the autotransformer such that full broad-band frequency response can ybe completely it permits tuning in a broad-band application whereas conventional tuning has been for tuning to a resonant frequency in a narrow-band application.

The windings of the autotransformer 155, like those described above, are tightly wound onthe core thereof with close spacing between the turns. As described above, the autotransformer of this and the other stages have a high primary-to-secondary,coupling coeiiicient, and a high side-to-side coupling coefficient. Actual primary-to-secondary coupling coefficients (KPS) of up to 0.98 andy side-to-side coupling coefficients K22 of up 'to 0.94 have been obtained at video-frequencies. Also,

` to-secondary coupling coefficients of only up to about n0.85 and side-to-side coupling coefiicients of up to only about y0.75. Air core autotransformers are accordingly Y utilized. This variable gap spacing has the advantage that rfilament transformers 185 and vention. The autotransformer of this invention is also advantageous over iron core transformers because the latter cannot be used for video-frequency applications on account of high distributed capacitance and eddy current loss. The frequency band aspect ratio (FBARJ miaX) f min.

of the radio-frequency power amplifier stages, in which this invention is employed, is very large for such a high power level. For example, an AM broadcast station at l mc./s. carrier frequency has a ratio of only.

Here, this ratio is A preferred transformer-coupled power amplifier interstage circuit design is to regard Vsuch circuits as pseudo- .low-pass LC ladder filter networks, where one or more of the series inductances and one or more of the shunt capacitances are contributed by the leakage inductances andl distributed capacitances respectively of the transformer itself.

. `This particular ferrite autotransformer 4configuration permits more precise design of LC filter interstage networks because a greater proportion of they associated filter sections are external to, and hence more readily controlled, than in former designs.

The output side taps of interstage autotransformer connect with the cathodes of the grounded-grid, pushpull, class B2 operated standard commercial power triodes 157 and 159, which are triodes such as the ML-6696 type, through low capacitance high leakage inductance 187, like those described above. To this end, one side tap of the autotransformer 155 connects with a center tap 188 of filament transformer and the other side tap of the autotransformer connects with a center tap 189 of the other filament transjformer 187. The transformers 185 and 187 have a suitable input power source such as a 460 v. A.C. power source as shown in FIG. 3. The outputs of the filament tion at their grids which are connected to each other and locked on ground. Triodes 157 and 159 are push-pull, class B2 operated triodes, such as the ML-6696 type, and their plates are connected to the cathodes of two more push-pull, class B2 operated triodes, such as F-6398 triodes, through an interstage autotransformer 191, like those described above, and having a suitable radio frequency ground and B+ source (not shown). This stage of amplification is similar to the stage that preceeded it, and the output high impedance plates of tubes 157 and 159 connect through autotransformer 191 and suitable filament transformers with low impedance cathodes of two push-pull, class B2 operated triodes 195 and 197 having their grids connected to each other and to ground. Here, however, the plates of triodes 157 and 159 are connected through a ferrite cored choke 193 like those described above for D.C. energizing and suitable capacitors are provided between the plates and the end taps of autotransformer 191.

V:sustraer The output plates of triodes 195 and 197 connect with the end taps of ferrite cored center-tapped autotransformei 199 like those described above. As mentioned, iowever, the windings thereof are hollow and have a cooling uid circulated therein, as are the windings of 191. The center tap of autotransformer 199 of radio frequency grounded vthrough a suitable capacitor and `has a suitable B-lsource. The output side taps are connected by coaxial cables 201i to suitable push-pull amplifiers such as amplifiers 201 (FIG. 2), which are connected with the accelerating cavity gaps of accelerating means 27, of the described high energy particle accelerator 11.

In operation atomic particles are injected into tube 13 at predetermined energies, speeds, pulse widths and angular spreads. Magnetic means Z6 bends the particles into a circular beam and focuses the beam in tube 13 and accelerating cavity gaps 27 are energized to accelerate the particles. Since the frequency tolerances that must be met by the cavity gaps 27 are so exacting, the programined cycle of conventional machines has been impractical. Accordingly, in the apparatus described herein, the proton beam in tube 13 provides the necessary information to control the frequency. To this end, a low level radio frequency system having an induction pick-up 42 around tube 13 which picks up an electrical signal each time a bunched beam of particles passes the pick-up, detects the correct frequency from the beam itself, means 4d corrects the phase so that the particles can be accelerated properly and supplies a low power command signal in cable 43 to amplier 44. The amplifier 44 boosts the power of the signal and supplies the boosted signal to twelve accelerating stations, each having a twenty-five kw. push-pull amplifier 201 and a double tunable radiofrequency loaded ferrite cavity 27 having a pair of gaps as described above, which imposes accelerating forces on the proton bunches at each passage of the gaps to produce protons with up to over 31 billion electron volts.

Amplifier 41 provides stable, pure wave, broad-band,

'video-frequency signals for amplifiers 2tl1 corresponding substantially linearly in amplitude and phase response to a relatively low power broad-band video-frequency command input signal in cable 43. For example, an output of 80 peak kilowatts, 120 peak radio-frequency amperes, and 1400 peak radio-frequency volts over a frequency 'range of from 1.4 to 4.46 megacycles per second is supplied to amplifiers 201 by amplifier 44 from a 1 watt 2 volt 1.4 to 4.46 megacycles per second input in cable 43. To this end, phase invertor 63 converts the single-ended input in cable 43 into a double-ended signal and supplies autotransformer 31. 'Autotransiormer 81 energizes pushpull, pentodes 106 and 107 having cathodes with a suitable direct current source connected therewith through Ylead 108 and the output from the plates of tubes 166 and 167 is a low impedance, push-pull, balanced-to-grouiid, broad-band, video-frequency signal corresponding in phase and amplitude to the input from cable 43.

The output from tubes lilo and 167 energizes further amplification stages having cascaded push-pull, balancedtti-ground, low impedance input, high impedance output, multi-grid tubes 199 and 111, 117 and 119, 125 and 127, and 133 and 135, having interstage center-tapped ferrite cored autotransformers 115, 123, 131 and 143, like the described auto-transformer S1 with their center-taps energized from a suitable source (not shown) through connections as shown in FIG. 3. Tubes 117 and 119, and 125 and-127 have suitable cathode followers as described and ferrite chokes `129, 137 and 145 clean up the wave form in the last three stages of section 46. The output from amplifying section 46 thus is a double-ended, push-pull, broad-band, video-frequency, high impedance source which corresponds in amplitude and phase with the cornmand input in cable 43 and the multi-grid tubes of the amplifying section 46 keep output radio-frequency cable 'termination phase perturbations of the section 54 from tailing back from the triodes of section 54.

. S, with a pure wave form. Likewise, the outputs from triodes 157 and 159 are amplified further in autotransforiner 191 which connects triodes 157 and 159 with triodes 195 and 197 and in autotransformer 199 which connectsftriodes 195 and 197 through leads 20@ with amplifiers 201 which are like the described grounded-grid amplification stages. Also tuning means is operable to adjust the impedance of the described autotransformers.

From the above, it will be understood that there are numerous applications in the fields of nuclear physics research and communications that require broad-band high power output, video-frequency amplifying systems and it will be understood from the above that the autotransformer of this invention can be used advantageously in such fields.

It is also understood that the foregoing has emphasized the utility of the autotransformer of this invention in balanced circuitry but the autotransformer of this invention is also useful in single-ended applications.

The system of this invention provides a simple, relatively inexpensive and effective means for supplying in a high energy accelerator a high power, broad-band, stable, video-frequency signal corresponding precisely in amplitude and phase with a relatively low power, broad-band video-frequency input. The system of this invention has the advantage of low cost, effective, simple, components, standard power triodes in the upper stages thereof, standard tetrodes in the lower stages thereof, and permits the use of a reduced number of commercially available high power electron tubes, relatively low direct current anode potential, minimized direct current anode power input, and minimized electrode dissipations. This invention additionally provides an autotransformer for interstage coupling in a truly broad-band video-frequency amplifier and provides an impedance match between a high impedance driving anode and a low impedance driven cathode 'that has not been possible heretofore so that the described combination with the described inherently stable grounded-grid configuration produces high power, broadband, video-frequency amplification with good transient response.

l claim:

rl. An amplifier for supplying high power, broad-band, video-frequency signals in a high energy particle accel- ,erator having particle accelerating means connected to .Y said amplifier, comprising an amplifying stage having tor, and tightly-wound, closely-spaced, center-tapped,

voltage-step-down windings around said core for preventing output termination phase perturbations from tailing back from said triodes.

2. An amplier for supplying high power, broad-band, video-frequency signals in a high energy particle accelerator having particle accelerating means connected to said amplitier, means for providing a low power singleended signal corresponding in phase and amplitude to the speed of said high energy particles first amplifying stages for said signal having low power output push-pull connected grounded cathode multigrid tubes, second amplifying stages having high power output push-pull connected grounded-grid triodes, and interstage autotransformers for coupling and amplifying the output of the stages of said amplifier for supplying said output to said accelerating means withlinear phase and amplitude response to said low power signal, comprising a split-ring-shaped ferrite core forming gaps that bisect said core in a plane that is normal to the plane of said core and coincides with the axis of said core, said ferrite having a high permeability and a low power loss factor, and tightly-wound, closelyspaced, center-tapped, voltage-stepdown windings around said core and extending equal distances in opposite directions from a point on said core equal distances from said gaps.

video-frequency signals in a high energy particle accelerator having particle accelerating means connected to said amplifier, comprising first amplifying stages having low power output push-pull connected grounded cathode tetrodes, second amplifying stages having high power output push-pull connected grounded-grid triodes, and interstage autotransformeis for coupling the stages of said amplifier in a cascade, comprising a split-ring-shaped ferrite core forming gaps that bisect said core in a plane that is normal to the plane of said core and coincides with the axis of said core, said ferrite having a high permeability and a low power loss factor, means for equally varying the opening in said gaps in said core, and tightly-wound, closely-spaced, center-tapped voltage-step-down windings 3. An amplifier for supplying high power, broad-band,

around said core and extending equal distances in opposite directions from a point on said core equal distances from said gaps wherein said windings have a high side to side coupling coefficient and a high through coupling coeiiicient.

4. An amplifier for supplying high power, broad-band, video-frequency signals in a high energy particle accelerator having particle accelerating means connected to said amplifier, comprising amplifying stages having low 4power output, push-pull connected grounded cathode tetrodes, amplifying stages having high power output pushpull connected grounded-grid triodes, and interstage autotransformers for coupling the stages of said amplifier, comprising a split-ring-shaped ferrite core having adjacent coaxial semi-circular segments forming gaps that bisect said core in a plane normal to the plane of said core that coincides with the -axisr of said core, said ferrite` having a permeability of over 300 and a quality factor of over 2O at 1.4 megacycles per second, means for equally opening and closing said gaps in said core, tightly-wound hollow closely-spaced, center-tapped, voltage-step-down windings around said core and extending equal distances in opposite directions from a point on said core equal distances from said gaps, and means for circulating a coolant through said windings.

5. Apparatus for supplying broad-band, video-frequency high power output signals, comprising abroadk band, video-frequency low power energy source, a iirst amplifying section having low'power output push-pull connected grounded'cathode tetrodes connected to said source, a. second amplifying section having high power output push-pull connected grounded-grid trodes, and interstage inductors for coupling the sections of said amplifier, comprising a split-ring-shaped ferrite core forming gaps that bisect said core in a plane normal to the plane of said core that` coincides with the axis of said core, said ferrite having a permeability of over 300 and a qualityy factor of over 20 at 1.4 megacycles per second, means for equally opening and closing said gaps and tightlywound closely-spaced, center-tapped voltage-step-down windings around saidcore and extending equal distances lin opposite directions from a point on said core equal distances from said gaps for connecting said stages through said inductors for providing high stage gain and smoothness of phase-frequency response.

6. Apparatus for amplifying broad-band, video-frequency high power signals, comprising at least two grounded-grid push-pull, high power output amplifying stages having triodes, and interstage inductor for coupling said amplifying stages in a cascade, ycomprising a splitring-shaped ferrite core formed with gaps in a plane that bisects said core normal to the plane of said core, said ferrite having a high permeability and a low power loss factor, means for maintaining an equal opening in said gaps in said core, and tightly-wound, closely-spaced, center-tapped,,voltage-step-dowri windings around said core and extending equal distances in opposite directions from a point `on said core equal distances from said gaps for connecting said stages through said inductors for providing high stage gain and smoothness of phase-frequency response.

7. Apparatus for supplying broad-band, video-frequency, high power output signals, comprising a broadband, video-frequency, low power energy source, first amplifying stages having low power output, push-pull connected grounded cathode tetrodes connected to said source, second amplifying stages having high power output, push-pull connected grounded-grid triodes, and interstage inductor for coupling the stages of said amplifier in a cascade, comprising a split-ring-shaped ferrite core formed with gaps that bisect said core normal to the plane of said core, said ferrite having a high permeability, a low power loss factor, means for maintaining an equal opening in said gaps in said core, and tightly-wound, closely-spaced, center-tapped, voltage-step-down windings around said core and extending equal distances in opposite directions from a point on said core equal distances from said gaps for connecting said stages through said inductors for providing high stage gain and smoothness of phase frequency response.

8. An interstage autotransformer for coupling amplifying stages in an amplifier operable to supply high power, broad-band, video-frequency outputs, comprising a splitring-shaped ferrite core forming two opposite gaps that bisect said core in a plane normal to the plane of said core and coinciding with the axis of said core, said ferrite having a permeability of over 300 and a quality factor of over 20 at 1.4 megacycles per second, means for equally opening and closing said gaps, and tightly-wound, closelyspaced, center-tapped voltage-step-down windings around said core and extending equal distances in opposite directions from a point on said core equal distances from said g An interstage autotransformer for coupling amplifying stages in an amplifier operable to supply high power, broad-band, video-frequency outputs, comprising a splitring-shaped ferrite core formed with gaps in a plane that bisects said core normal to the plane of said core, said ferrite having a high permeability and a high power loss factor, means for maintaining an equal opening in said gaps in said core, and tightly-wound, closely-spaced, center-tapped voltage-step-down windings around said core and extending equal distances in opposite directions from a point on said core equal distances from said gaps.

10. In a power amplifier :for use in a high energy particle accelerator requiring high power, broad-band, videofrequency signals and having cascaded push-pull connected grounded-grid triode amplilication stages, prior push-pull connected, cascaded grounded-cathode tetrode amplification stages that are connected with said triode stages and are operable to keep output cable termination phase perturbations from tailing back from said grounded-grid triode stages, high permeability, low power loss factor ferrite cored interstage chokes for smoothing wave forms between said stages, and a low-power, broad-band, videofrequency command signal input for said stages, a ferrite cored interstage autotransforrner between each of said stages, comprising an annular core having a permeability greater than 300, a quality factor of at least y20, tightly wound, center-tapped, voltage-step-down windings around said core, and opposite equally adjustable gaps equally spaced from said windings so that substantially all the lines of force produced by said windings remain in said core and said autotransformer has high through coupling 15 coeicients and high side-to-side coupling coefficients whereby a simple, easily cooled, easily shielded circuit havingstandard vacuum tubes is provided that supplies high power, broad-band, video-frequency signals that substantially linearly correspond with the phase and frequency of said command signal.

References Cited in the le of this patent UNITED STATES PATENTS Giblin Jan. 26, 1932 10 11i Friis et al May 24, 1932 Bohm Oct. 20, 1936 Masterson Oct. 3, 1950 Hare July 24, 1951 Green Nov. 13, 1951 Bessey May 12, 1953 FOREIGN PATENTS Sweden Sept. 13, 1955 

1. AN AMPLIFIER FOR SUPPLYING HIGH POWER, BROAD-BAND, VIDEO-FREQUENCY SIGNALS IN A HIGH ENERGY PARTICLE ACCELERATOR HAVING PARTICLE ACCELERATING MEANS CONNECTED TO SAID AMPLIFIER, COMPRISING AN AMPLIFYING STAGE HAVING PUSH-PULL CONNECTED GROUNDED CATHODE TETRODES, AN AMPLIFYING STAGE HAVING PUSH-PULL CONNECTED TRIODES WITH GROUNDED GRIDS, AND INTERSTAGE AUTOTRANSFORMER FOR COU- 